Even so, Friedmann is confident. "There's always a clue," he says. "All of these methods have molecular signatures that we will be able to detect."
Beyond genes, another booster looms: stem cells. Researchers around the world are growing these malleable cells into all sorts of tissue, from muscle to nerve to bone. In theory, stem cells could be used to augment an athlete in ways similar to gene therapy. Most scientists say stem cell technology isn't yet advanced enough for athletic use. But last month, German journalists released a documentary showing a Chinese doctor offering to inject stem cells into a swimmer for $24,000.
Was the doctor making a legitimate offer? "There's no way to know," says Friedmann, "but nothing would surprise me."
